Angiogenesis, or the remodeling of preexisting quiescent blood vessel, is critical for embryonic development, wound healing, and various pathological conditions including tumor progression and atherosclerosis. We propose to study in molecular terms, the function of phosphatidic acid phosphatase 2b (PAP2b), a plasma- membrane protein that we discovered in a functional assay of angiogenesis. The PAP2b protein is expressed by endothelial cells, exhibits a cell adhesion sequence, and dephosphorylates phosphatidic acid phosphate (PAP) into diacylglycerol and phosphate, that has been implicated in signal transduction and lipid metabolism. The Pap2b gene inactivation is early embryonic lethal (die around E7.5 day) due to lack of functional vasculature. PAP2b is the first lipid phosphate phosphatase protein that is linked to the Wnt signaling pathway. We found that PAP2b is expressed by a subset of primary tumors, and over-expression of PAP2b supports tumor growth and angiogenesis. We observe that PAP2b interacts with p120catenin and promotes cell-cell-interactions, in turn, induces protein complex formation between beta-catenin and lymphoid enhancer-binding factor-1 (LEF-1), this event leads to fibronectin and IL-8 synthesis and secretion. Based upon our preliminary data, we hypothesize that during angiogenesis PAP2b plays a key role in the formation and organization of adhesion structures connecting endothelial cells. The mechanisms include the ability of PAP2b to form and organize large molecular complex, interact with a subset of integrins, and mediate synthesis of fibronectin through LEF-1 transcriptional machinery. The overall aim of this proposal is to determine the mechanism by which the PAP2b interacts with p120catenin, and mediates synthesis of fibronectin. We propose to test our hypothesis through two major specific aims: (1) Characterize the mechanism by which PAP2b interacts with p120catenin, alter LEF-transcription, and induce expression of fibronectin and IL-8, and (2) Examine the functional consequences of conditional deletion of Pap2b gene in the mice using Tie-2/Cre system. Examine the consequences of SiRNA mediated down-regulation of PAP2b using endothelial cells. We anticipate that our studies will further our understanding of the role of endothelial PAP2b in physiological and pathological angiogenesis. Together, these studies are expected to reveal a new target for anti-angiogenic molecular therapy.